A new study in the Journal of the American Dental Association finds once again that, contrary to what most people have been told, fluoride is actually bad for teeth.

Exposure to high levels of fluoride results in a condition known as fluorosis, in which tooth enamel becomes discolored. The condition can eventually lead to badly damaged teeth. The new study found that fluoride intake during a child's first few years of life is significantly associated with fluorosis, and warned against using fluoridated water in infant formula.